Pushrod Tech

Prior to extensive research at COMP Cams®, it was thought that the pushrod only had to be strong enough not to fail, bend or burn up at the ends. But engineers have learned that the frequency of the pushrod must match that of all the rest of the parts in the valve train, as well as the rpm at which the engine will be run.

As cam profiles get more aggressive and valve spring pressures increase, the importance of selecting the right pushrods has never been more critical. COMP Cams® carries a wide selection of precision pushrods to handle any application from stock replacement to hardcore race.

Pushrod Length & Rocker Arm GeometryMeasurement Techniques

A large number of variables are involved in determining the correct length pushrod for your application. Pushrod length is affected by any of the following:

Block deck height

Head deck height

Head stud boss height

Rocker arm brand/design

Cam base circle size

Lifter design/brand/pushrod seat height

Valve stem length

Don't assume anything when determining the right pushrod for your new engine. A pushrod that fi ts one engine may not necessarily work in another. Any number of items can be different on your engine, requiring you to use a different pushrod length. Following the steps below will streamline the pushrod selection process, ensuring that you get the right parts the first time.

1. Buy a checking pushrod.
Invest in a checking pushrod. They are on page 295 of this
master catalog. They are available in two different designs, with
the more expensive of the two being easier to measure once you
have it adjusted to the proper length for your valve train. Neither
is particularly expensive if you consider time lost and freight costs
when returning pushrods.
Other companies offer their own versions of pushrod length
checking devices, plastic pieces with complicated instructions to
calculate the length. The main disadvantage with these is that you
have to order the pushrods and receive them before you know if
your calculations are correct. With a checking pushrod, you can
actually rotate the motor over and check the rocker arm/valve tip
relationship as you adjust the pushrod length. When you get the
correct geometry, it is a simple matter then to measure the length
and place an order. COMP Cams® carries a large number of various
length and diameter pushrods.

2. Determine correct valve train geometry.
What is the correct length pushrod for your application? The one that
produces correct valve train geometry. What is correct valve train
geometry? When the rocker arm roller tip rolls from the intake side of
the valve tip, across the center of the tip (at approximately mid-lift), to
the exhaust side of the valve tip (at full lift) and back. See Diagram A.

3. Measure the resulting pushrod.
Measuring the length of a pushrod is a simple process. The most
important thing to remember is that different manufacturers measure
pushrods differently. Not all pushrods of a stated length will measure
exactly the same. The three most common pushrod measurements
are shown in Diagram B on the following page.

Theoretical Length: This assumes that the pushrod has no oil hole
in the end of it. Therefore, the radius at either end is complete, which
lengthens the pushrod approximately .017" in the case of a 5/16"
pushrod with .100" diameter oil holes, minimally chamfered.

Actual Length: This is what you would measure if you had a set of
calipers large enough to measure over the oil holes at each end of
the pushrod. This is the measurement that most people can relate to.
Unfortunately, this measurement is affected not only by the diameter
of the oil holes but also by the entrance chamfer for each oil hole.

Gauge Length: Although the most difficult to measure (it requires a
special length checking gauge), this measurement is the most reliable.
This is because the oil holes and their chamfers are eliminated from
the measurement. The only problem is that not all companies use the
same gauge diameter. COMP Cams® uses a .140" gauge diameter. All
Magnum and Hi-Tech™ Pushrods listed in this catalog are measured
using this technique. See Diagram B on the following page.

4. Simple measurement techniques.
We realize that most people don't have access to the special gauge
required for these measurements or even a dial caliper large enough
for most pushrods. We've developed two techniques to help you
determine exact pushrod length so that the perfect valve train
geometry is achieved in your engine.

Technique #1
This technique requires the use of a COMP Cams® Hi-Tech™ Pushrod
Length Checker. These are marked with a standard length stamped
in them. This number represents the gauge length of the part (.140"
gauge diameter) with the two halves screwed completely together. Extending
the pushrod one rotation lengthens the gauge length .050". For
example, a pushrod stamped 7.800" and screwed apart one rotation
would be 7.800" + .050" = 7.850" gauge length. Therefore you would
order the part number from the catalog that matches this gauge length,
since gauge length is how they are listed.

Technique #2
This technique requires one of our Magnum Pushrod Length Checkers.
Once fixed, you don't need to have an expensive gauge or a pair of
calipers to measure it. You just need a pushrod of a known length to
compare it to (a standard). Then use a pair of common 6" calipers to
measure the difference between the standard and yours.
Here are a few final hints about pushrods in general. It is always a
good idea to buy a few spares when purchasing a set of custom length
pushrods, and stick them in your toolbox. If one ever fails at the track
and you need a replacement, it would be nearly impossible to borrow
one from a fellow racer.

Another hint involves cup end pushrods. Measuring them for length
is especially difficult, no matter which technique above you choose to
use. The size and shape of the cup end varies greatly from manufacturer
to manufacturer, so measuring from the ball end to the cup end over
the cup surface is a dangerous practice. The best strategy is to drop a
5/16" diameter steel ball into the cup end, and do all measuring over
this ball, subtracting the 5/16" diameter (.3125") to figure the length.

COMP Cams® Pushrods

High Energy™

Number one choice when building street rods, RVs or daily driver applications

Available in 3/8" and 5/16" diameters

Designed to mate perfectly with High Energy™ and Magnum Rocker Arms

Meets or exceeds all original equipment pushrod specifications

Available in 3/8" and 5/16" diameters, High Energy™ Pushrods from COMP Cams® are an affordable, high quality solution when building street rods, RVs and daily drivers. High Energy™ Pushrods have a durable construction that meets or exceeds all OE pushrod specifications and fit perfectly with High Energy™ and Magnum Rocker Arms. With multiple end types are available, there is a High Energy™ Pushrod to fit your needs.

Magnum

Designed and heat-treated for extended durability and guide plate compatibility

Precision formed, reinforced pushrod ends

Black-oxide finished with easily read, laser-etched part number and length

Street performance and mild race engines

The Magnum 5/16" and 3/8" Pushrods offer an affordable solution for your .080" wall chromemoly pushrod needs. Designed to withstand the stresses of a high performance engine, these pushrods are heat-treated for extended durability and may be ordered as single pieces or in sets of 8 and 16. Multiple end types are available to fit virtually any application. All Magnum Pushrods are black-oxide finished and come with laser-etched part number and length for easy identification.

Prior to extensive research at COMP Cams®, it was thought that the pushrod only had to be strong enough not to fail, bend or burn up at the ends. But engineers have learned that the frequency of the pushrod must match that of all the rest of the parts in the valve train, as well as the rpm at which the engine will be run. Today's all-out race engines demand the highest quality components at every step, and COMP Cams® Hi-Tech™ Pushrods fill that requirement.

The one-piece design from .080" wall seamless chromemoly tubing ensures the ultimate in strength and durability. The ends are precision formed, yielding added thickness in the critical tip area for strength while maintaining constant wall thickness and concentricity. The pushrods are then heat-treated to ensure compatibility with guide plates and for maximum strength. They are OD-ground for consistency and black oxide-finished with their length and part number laser etched on the OD for ease of identification.

Semi-Finished

Many components also available in 200 and 400 piece Engine Builder Kits

Constructed from durable steel alloy and black-oxide finished

Semi-finished, multi-piece pushrods allow you to personally craft the exact pushrod needed for your high performance application. Simply choose your desired shaft length, shaft diameter, wall type, wall thickness, ball end diameter and end type. Many components are also available in 200 and 400 piece Engine Builder Kits. When ordering semi-finished pushrods, you must also order the proper pushrod cutter. Because there are so many variables involved, to order you must contact a trained COMP Cams® technician, who will help you order your semi-finished, multi-piece pushrods.

5/16"3/8"7/16"7/16" Dual Taper

To order Semi-Finished Pushrods you MUST contact CAMHELP® in either of the following ways:

COMP Cams® checking pushrods make it easy and economical to lay out and determine proper pushrod length during any high performance engine rebuild. Precise length measurement is necessary for correct valve train geometry in order to obtain the desired results from the cam and to ensure damage is not done to the rest of the valve train. Both Magnum and Hi-Tech™ Checking Pushrods are precision-crafted from a durable steel alloy and black-oxide finished to provide years of accurate measurement.

COMP Cams® carries everything required for cleaning and assembling custom pushrods. COMP Cams® Pushrod Cutting Bits are made specifically to cut pushrods and leave a .002" to .003" press fit between pushrod and tip. For maximum precision, use the Pushrod Holder to stabilize pushrods as they are being cut. The Pushrod Assembly tool works with cup and ball tips and allows for easy assembly while reducing the risk of splitting or bending pushrods. Thoroughly clean the internal oil passages of a center oiling pushrod with the COMP Cams® Pushrod Cleaning Brush. Tough enough to withstand repeated use, the Pushrod Cleaning Brush is designed to fit perfectly in any COMP Cams® Pushrod.